1. Field of the Invention
Methods and apparatuses consistent with the present invention relate to measuring dielectric characteristics of a dielectric having high dielectric loss, and more particularly, to non-invasive measurement of blood glucose concentrations by millimeter waves.
2. Description of the Related Art
Diabetics have suddenly increased in number due to lack of physical activity and changes in eating habits. The deaths caused by diabetes in 2001 in Korea are 23.8 people per hundred thousand people, and diabetes now stands fourth in causes for death in Korea. This rate has more than doubled since 1990. Individual diabetics must measure blood glucose by themselves due to the increase in number, i.e., self-monitoring of blood glucose is required. The self-monitoring of blood glucose is an important component of modern therapy for diabetes mellitus and offers detailed information about blood glucose levels at many times points to enable maintenance of more constant glucose levels in everyday life. As a general rule, most patients with type 1 diabetes are recommended to test their blood glucose level at least three or four times per day. However, it is reported that only 18% of diabetics periodically measure blood glucose, even in the U.S.A. which has a good social welfare. Such negligence of the self-monitoring of blood glucose is due to current invasive-type glucose meters which require blood samples directly taken from the body. Periodical tests by the invasive method not only gives pain or uncomfortable feelings during taking of the blood sample, but also imposes mental and economic burdens with considerable costs of consumable accessories necessary for taking the blood samples.
Devices for the non-invasive measurement of blood glucose have been developed to solve such pain and displeasure during taking blood and smoothly perform self-monitoring of blood glucose. As non-invasive measurement methods of blood glucose, methods of using an analysis of an absorption spectrum in an infrared zone and a method of using impedance spectroscopy in a band of tens to hundreds of MHz have been studied. Some prototypes or products have been researched and developed according to the above-mentioned method. To observe the validity of the non-invasive measurement of blood glucose in a millimeter wave band, dielectric characteristics of a glucose-0.9% NaCl solution depending on a glucose concentration in a band between 30 GHz and 40 GHz are investigated using an open-ended coaxial line method and a transmission coefficient measurement method.
To non-invasively measure the dielectric constant e′ and dielectric loss e″ of dielectric materials having a high dielectric loss in a millimeter wave band, the modulus and phase of the reflection coefficient of the reflected electromagnetic wave from the dielectric object are generally measured according to the open-ended coaxial line method using a vector network analyzer. However, it is known that a measurement accuracy of the dielectric constant e′ using the vector network analyzer is on a level of ±5%. The main problem with solids is the contact between the coaxial probe and the material under test, which causes inaccuracy and low reproducibility of the measurement. According to the experimental results performed in the frequency band between 30 GHz and 40 GHz, the variations of 0.3 to 0.6 in the dielectric constant Δε′ of the glucose-saline solutions having the dielectric constants between 20 and 30 have been reported. However, such a precise measurement is impossible in consideration of the measurement accuracy of the vector network analyzer.